Hydra IRC bot, the 25 minute overview of the kit.

Hydra IRC bot, the 25 minute overview of the kit. (25 minutes to write and “do”, not to read!)

The Hydra IRC botnet kit is a very interesting sample that we have in our collection. It is, essentially, “RX-Bot for Routers”. By this, we mean it is an extensible, well documented (in the source), open source botnet framework which is freely available for anyone to download. The problem, of course, is locating a copy.

Unlike other IRC bots targetting the “Linux” platform, for example, the “Kaiten” series of bots written in C, or the “ShellBot” series of bots written in various scripting languages, the Hydra is a more carefully developed framework, and by design is far more extensible than the others.

While the Kaiten family offer potent DDoS capabilities, they totally lack spreading tools – in order to “spread” a Kaiten effectively, you would have to root Linux servers en-masse. The Hydra, has built in worm-like capabilities, allowing it to automatically seek out and infect new victims.

The shellbots DO spread, and may even infect other platforms/architectures (being written in scripting languages means they will run on anything that has an interpreter), however their DDoS capabilities are weak, and they tend to be rather “hacky” programs.

Furthermore, while the Kaiten bots are almost limited to the x86-Linux platform (they stubbornly refuse to compile on much else), the Hydra series is designed to run on damn near anything – in particular, MIPSEL routers.

Most interesting of all, however, is the fact that the development of these elegant pieces of malware has not progressed much. Wheras the Kaiten and Shellbot are constantly being remade, the Hydra, being a far more impressive – and complex – piece of code, is pretty much ignored by your contemporary developer of Unix malware. This is unusual, as its counterpart on Windows – RXbot, was developed almost religiously.

Anyways, on we go. Lets crack open the archive and see what is inside!

As you can see, it is a fairly well-crafted piece of software, in that the developers did not try jam everything in one source file, like the developers of Kaiten and the ShellBots do. Instead, everything is split up rather neatly. This would make future development FAR easier than hacking on one file!

So, it would seem that this was the “first release of 2008”. And the changelog itself makes me think the developer was doing some serious work on it – rewriting the source code completely, fixing bugs, removing useless functions and commands… It makes me wonder were there previous variants that I have simply not obtained yet.

Onward we go to the Makefile, and for brevity I only include the relevant snippet here – the rest is pretty much “normal”.

So, we can clearly see, this version supports the MIPSEL and x86 architectures, and I do wonder who “hardhat” is… Don’t you?

The fact the author wrote a somewhat decent makefile suggests either an IDE of some kind that auto-generates them for you, or, a somewhat competent author. Having had difficulty getting ANYTHING to run on MIPSEL routers in the past, I will go with “competent”.

Lets take a look at the readme, see if we can gather more data! As @TheResGroup says, “we love data”.

First off, the author is not a native English speaker. Second, his email is proudly on display as “esaltato@autistici.org”. I checked autistici.org, it seems to be some kind of Privacy collective, similar to Riseup.net (who, by the way, are AWESOME). It also makes me think of Italy, and there is more evidence for this later on when we see the predefined C&C server.

In the readme, he describes his program in the following manner:
“Hydra is a mass-tool commanded by irc that allows scanners and exploited dlink router for make BOTNET (rx-bot style), in addition to this, with void you can attack with tcp/udp flood.”
Ok, so we know his intention – an RX Bot style bot for routers, in particular, D-Link routers. Now, unless I am terribly mistaken, the D-Link routers run DD-WRT of some kind, which is basically MIPSEL Linux. Which is why this bot works so damn well.

The interesting thing is, he does NOT give a command list in the readme! So the user could setup their botnet, then realize they have NO clue how to use it!

So. While the README tells us we have both UDP/SYN flooding, the commands only offer SYN. Which makes me assume we are missing some commands! Having poked through the source, the UDP flooding functionality is simply not there, so I assume it is not implemented in this version.

Now that we have an overview of the bots capabilities, let’s take a look at the DDoS code in it, before I wrap this post up. Please note – this post is essentially a “teaser” of a paper me and a fellow researcher are writing on this kind of malware, and trust me – that paper is gonna be badass.

As we can see, it is sending a SYN packet, with a window size of 512, to a specified port. It uses its PID as the sequence number and has an offset of 5. Surely a detection could be written, but I am sure it would be littered with false positives.

Now, I am not an expert, but the following snippet makes me think maybe it is threading the function to run 50 times – I do not see any calls to fork(), but it seems to have a loop here that increments a counter (vt) every time a thread runs.

It would appear that this snippet runs a counter, which SYN floods with 50 threads for X time, and alerts the IRC room when it is done. Fairly standard fare for an IRC bot, however most thread numbers I see are 64/128/256 in other bots/DDoS tools. Likely they use less threads due to the limited CPU capabilities of embedded devices, or, maybe the programmer just wanted to use 50 threads…

This concludes my “brief writeup” on the Hydra, and in an upcoming paper I will be covering it in more depth – including its propagation mechanisms and other interesting things that we find, including the hardcoded C&C, configuration settings, and such.